A block copolymer comprising different kinds of polymer segments expresses properties of the different polymer segments themselves. Therefore, the block copolymer is useful as an adhesive agent, a polymer surfactant, thermoplastic resin, or the like. For example, it is reported that an adhesive composition which contains an A-B type block copolymer comprising a polymer A containing an alkyl(meth)acrylate monomer having an alkyl group having 4 to 12 carbon atoms and a polymer B containing at least one selected from the group consisting of vinyl acetate, methyl acrylate, methyl methacrylate, styrene, and acrylonitrile has high adhesive properties and removability to a flat substrate, and therefore, the adhesive composition does not remain on the substrate after removing (Patent Document No. 1).
In addition, it is also reported that a composition which contains a thermosetting resin and powder or granular A-B type block copolymer comprising a segment A containing a vinyl polymer having a glass transition point of −60 to −20° C. and a segment B containing a vinyl polymer having a glass transition point of 50 to 130° C. has excellent fluidity, and a mold made of the composition has excellent impact resistance and appearance (Patent Document No. 2).
In addition, it is also reported that when an A-B-A type block copolymer containing poly-N-isopropyl acrylamide-poly-N,N-dimethyl acrylamide-poly-N-isopropyl acrylamide is heated to the phase transition temperature (about 32° C.) or more in water, the segment A transfers from hydrophilic to hydrophobic, and thereby the block copolymer is self-coagulated (Non-Patent Document No. 1).
It is considered that the A-B-A type block copolymer is hydrophilic when it is at a temperature less than the phase transition temperature, and does not have adhesive properties to the substrate. However, when it is at the phase transition temperature or more, the segment A transfers to hydrophobic, and thereby has high protein adsorption properties.
In addition, an amide block copolymer which comprises a block made of a repeating unit derived from N,N-dimethyl acrylamide and N-methyl acrylamide and a block made of a repeating unit derived from (meth)acrylic ester monomer having a hydroxyl group or a styrene monomer having a hydroxyl group is useful as a coating agent for a leucocyte-removing filter which can transmit platelets with high transmittance (Patent Document No. 3).
Furthermore, it is also reported that a star block copolymer made of methoxyethyl(meth)acrylate and N-isopropyl acrylamide is water-soluble when it is at the phase transition temperature or less, and becomes hydrophobic when it is at the phase transition temperature or more, an aqueous solution of the star block copolymer at low temperature is coated to a medical instrument, and then the temperature is raised to the phase transition temperature to attach the star block copolymer to the medical instrument; and this technique is used in an antithrombotic instrument (Patent Document No. 4).
As a medical instrument, a polymer (for example, polyolefin resin, such as polypropylene and polyethylene, polyvinyl chloride, polyurethane, polystyrene, polyester, polysulfone, polytetrafluoroethylene), ceramic, metal, and the like, which have high mechanical properties (strength, modulus of elasticity, and ductility) have been used as a main part or a connection part according to the purpose. In particular, it is essential that a medical instrument which is used to directly contact with blood (for example, a catheter, such as a balloon of a balloon catheter, and a guide wire, an artificial blood vessel, a blood vessel bypass tube, an artificial valve, a blood transfusion filter, a plasma separation device, an artificial internal organ, such as an artificial lung, an artificial liver, and an artificial heart, a blood transfusion tool, an extracorporeal circulation blood circuit, a blood bag, a synechia preventive film, a vulnerary covering material, and the like) have blood compatibility with high reliability, in particular, antithrombotic properties for preventing blood coagulation.
However, many materials among those explained above do not have blood compatibility. Therefore, it is essential to use an anticoagulant (for example, heparin) at the same time. However, when influences on a human body or blood are concerned, the continuous availability time of the anticoagulant is limited. Therefore, there is a problem in that there is a time limit for medical activity using such a medical instrument. In order to solve the problem, medical instruments having excellent blood compatibility have been developed. Representative examples of such medical instruments include a medical instrument having a surface in touch with blood on which the anticoagulant such as heparin is immobilized.
However, it is known that when heparin is used, antithrombotic properties are decreased by elution of heparin, and infectious disease can be caused since heparin is generally animal-derived. Therefore, it is most desirable that a material having antithrombotic properties which is free from heparin be developed. However, it is required to utilize properties of various raw materials in the medical instrument. Therefore, it has been desired to develop an antithrombotic coating agent which can provide antithrombotic properties to a product or a part which is made of the raw material explained above.
There are two important factors regarding the coating agent which provides antithrombotic properties. One of them is that the surface coated with the coating agent shows excellent antithrombotic properties, and the other is adhesive properties to the raw material. Regarding the former, when platelets or proteins in blood are attached to the medical instrument, and are activated thereon, clots, so-called thrombus, are formed. There is a risk of severe brain infarction or pulmonary thromboembolism occurring by the thrombus flowing in the blood and being dispersed in the brain or lungs. How to prevent the thrombus formation reaction stably for a long time is a big problem for the antithrombotic coating agent.
In general, it has been considered that a surface having high energy and high wettability (low water contact angle) is suitable as a surface having antithrombotic properties which does not adsorb platelets and the like. For example, it is reported that a surface which is made of a hydrophilic polymer (for example, water-soluble copolymer of polyethylene glycol acrylate and acrylacrylate (Patent Document No. 5)), a copolymer of a hydrophobic monomer and a hydrophilic monomer (for example, a (meth)acrylate copolymer of hydrophobic silicone (meth)acrylate or alkyl(meth)acrylate and hydrophilic(meth)acrylate (Patent Document No. 6)), or hydrophilic hydrogel (for example, chemical crosslinking gel of poly(N,N-dimethyl acrylamide (Patent Document No. 7)) has inhibitory effects which prevent the adhesion of blood components. In addition, it is also reported that an amide block copolymer containing a block having a repeating unit derived from N,N-dimethyl acrylamide or N-methyl acrylamide, and a block having a repeating unit derived from a (meth)acrylic ester monomer having a hydroxyl group or a styrene monomer having a hydroxyl group is useful as a leucocyte-removing filter which transmits the platelets with high transmittance (Patent Document No. 3).
On the other hand, it is also reported that, as the coated material having antithrombotic properties, a member having a surface which includes a synthesized polymer such as methoxyethyl(meth)acrylate having no hydroxyl group prevents the adhesion and activation of the platelets and has antithrombotic properties (Patent Documents No. 8 or 9), and the member is useful as a leucocyte-removing filter (Patent Documents No. 10 or 11), and an artificial lung (Patent Document No. 12). Furthermore, it is also reported that a resin having a repeating unit of methoxyethyl acrylate, such as a block copolymer of methoxyethyl acrylate and N-isopropyl acrylamide (Patent Document No. 4), a block copolymer of methoxyethyl acrylate and glycidyl methacrylate (Patent Document No. 13), and a copolymer of methoxypolyethylene glycol(meth)acrylate and alkyl(meth)acrylate (Patent Document No. 14) can be used as the coating agent having antithrombotic properties. However, even the performance of these materials is insufficient as the coating agent having antithrombotic properties. The market has desired the development of a new excellent antithrombotic material which is free from heparin. In particular, an antithrombotic coating agent which has superior antithrombotic properties to those of a conventional antithrombotic coating agent and high adhesive properties to various substrates has been desired.